Operation of an Inductive Power Transfer System

ABSTRACT

The invention relates to method of detecting an arrangement having a primary unit of an inductive power transfer system and/or a secondary unit of the inductive power transfer system. The method including: using a detector device to detect the arrangement, the detector device having at least one electrical conductor, determining at least one electrical property of the detector device and generating determination results consisting of a determination result for each of different regions of the arrangement, and comparing the determination results with existing information about the arrangement to be detected. The existing information includes information about expected values for the different regions of the arrangement, thereby generating a comparison result, and deciding from the comparison result whether the determination results indicate that the detector device has detected the arrangement as expected.

The invention relates to the operation of an inductive power transfer(IPT) system. The invention includes (i) a method of detecting anarrangement, (ii) a method of operating an IPT system comprising themethod of detecting the arrangement, (iii) a primary unit arrangement ofan IPT system and (iv) a secondary unit arrangement of an IPT system.

The IPT system comprises a primary (side) unit with a primary windingstructure, which primary unit is located in particular on a route or ona stop (e.g. a bus stop or parking area) of a vehicle which can drivealong the route. The primary winding structure generates a magneticfield which is received by a secondary (side) unit of the IPT systemthat is also known as receiver or pick-up. In case of a vehicle, it maybe related to as on-board receiving unit (ORU). The secondary unit has asecondary winding structure. The primary and secondary windingstructures comprise windings of in each case at least one electricconductor. In between the primary winding structure and the secondarywinding structure, there is an air gap through which the generatedelectromagnetic field extends during operation. An electric voltage isinduced in the secondary winding structure and, while the secondary unitprovides power to any load, the load current through the secondarywinding structure generates a secondary electromagnetic field. Thiscurrent depends at least partially on the mutual induction between theprimary winding structure and the secondary winding structure. Theprimary unit and the secondary unit form an electrical transformer.

The IPT system can be used for static energy transfer or static chargingof a vehicle, i.e. the vehicle does not move during energy transfer. Inthis case, the primary unit can be designed as a so-called charging pad,which may be integrated into the route or mounted on the route surfaceas an elevated charging pad. Alternatively, the IPT system can be adynamic system transferring energy while the vehicle travels along thedriving surface of the route.

WO 2014/095722 A2 discloses a safety system for an inductive powertransfer system that transfers power to a vehicle on a surface of aroute, wherein the safety system comprises at least one inductivesensing system, wherein the inductive sensing system comprises multipledetection windings and wherein the multiple detection windings arearranged in an array structure, which at least partially covers acharging surface that is assigned to the primary winding. The safetysystem detects foreign objects, in particular metal objects, located inproximity of the primary winding structure.

The primary unit and the secondary unit of the IPT system compriseelectrically conductive parts, at least the windings mentioned above.Typically, they also comprise magnetic or magnetizable material, inparticular ferrites, for shaping the magnetic field of the IPT systemduring operation. Since there is an air gap between the primary unit andthe secondary unit, the units are movable relative to each other.Therefore, a vehicle having an on-board secondary unit can move to apredetermined position where the energy transfer from the primary unitto the secondary unit is optimal. Consequently, there is a need toensure that the secondary unit is actually in the optimal position. Forexample, mechanical means may be provided for this purpose. Anotheroption is a control device which controls positioning the vehicle basedon contactless detecting the relative position of the primary andsecondary unit.

The same primary unit may be used to provide energy to differentvehicles one after the other. For different reasons, there is a need todetect or recognize which vehicle or which type of secondary unit isactually positioned close to the primary unit. One possible reason isthat the billing for the energy delivered must be directed to thecorrect address. Another possible reason is that there may be differenttypes of secondary units and that the primary unit may be operated in adifferent manner depending on the type of the secondary unit which is tobe provided with energy.

Another aspect of operating an IPT system is the detection of undesired,foreign objects which are not part of the IPT system. According to WO2014/095722 A2, a safety system is provided for this purpose. Inparticular, if the foreign object is electrically conductive, it can beheated up rapidly, thereby becoming a dangerous hot object. In addition,the foreign object may deteriorate the energy transfer to the secondaryunit.

It is an object of the present invention to improve the operation of anIPT system with respect to at least one of the needs and requirementsmentioned above.

According to a basic idea of the present invention, each primary unitand each secondary unit of an IPT system has a specific structure whichcan be detected in a contactless manner, thereby detecting the unit ordetecting an arrangement comprising the unit and at least one furtherobject. A corresponding detection unit or detection arrangement cantherefore detect a signature of the unit or arrangement which ischaracteristic for the unit or arrangement. In particular, differenttypes of primary units and different types of secondary units havedifferent signatures. Depending on the precision of detecting thesignature, it is even possible to distinguish between different primaryunits of the same type or between different secondary units of the sametype. This may be facilitated by providing the unit with an individualfeature which is not present in all other units of the same type. Forexample, an electrically conductive and/or magnetizable part may beshaped and/or positioned in an individual manner in the unit.

The contactless detection performed by the detector device is preferableperformed by determining at least one electrical property. The propertyin particular corresponds to at least one physical quantity that ismeasured in order to determine the property. In particular inductiveand/or capacitive coupling of the unit or arrangement to be detectedwith the detector device can influence electrical properties of thedetector device. Therefore, the signature may be considered as amagnetic signature in case of inductive coupling and/or may beconsidered as an electrical signature in case of capacitive coupling.

In particular, the signature of the primary or secondary unit isobtained and therefor known before the unit or an arrangement comprisingthe unit is detected by the detector device. Depending on the furtherprocessing of the results of the detection, the signature can beobtained during a previous operation of the detector device or ofanother detector device of the same type or can be calculated usinginformation about the structure of the unit or arrangement. Thesignature can be stored in a data storage of the arrangement comprisingthe primary unit or the secondary unit. In addition or alternatively,the signature can be stored in a data storage of a central system whichcommunicates with the IPT system and preferably communicates with aplurality of IPT systems.

In particular, the signature and the detection results of the detectordevice can comprise information with respect to two local dimensions,for example with respect to two axes of a two-dimensional coordinatesystem. In this case, the signature and the detection result correspondto a two-dimensional image, similar to a photograph taken by a digitalcamera. Different regions of the unit or arrangement can be captured bythe signature or detection result, wherein the individual results of theregions correspond to pixels of a digital image or photograph. In thefollowing, they are referred to as pixels. Each pixel may have a singlevalue characterizing the material of the region of the unit orarrangement which is captured by the pixel. For example, typicalmaterials used for the primary unit and secondary unit are copper as thematerial of the windings, ferrite, plastic as electrical insulator andoptionally other metals, such as aluminum, for shielding the environmentfrom the fields of the IPT system. For example, each value of the pixelsmay indicate the material which is predominant in the captured region.The pixels may be arranged in rows and columns, wherein the number ofpixels in each row and each column may, for example, be a number in therange of 5 to 200. In any case, it is preferred that the signature andthe detection result have the same numbers of pixels in their rows andcolumns. However, this is not necessarily the case. For example, thesignature may have more pixels and areas comprising a plurality of thepixels may be combined so as to form a combined pixel in order tocompare the signature with the detection result.

It is also possible that the signature and the detection resultcorrespond to a three-dimensional image. This means that not only imageinformation with respect to two directions transverse to the viewingdirection is obtained by the detector device, but additional imageinformation with respect to the viewing direction. This additionalinformation can be obtained, since the inductive or capacitive couplingof the arrangement to be detected with the detector device depends onthe distance of the arrangement to the detector device. For example, thesame block of material (e.g. ferrite) of the secondary unit results indifferent values of the impedance of a detection element of the detectordevice depending on the distance to the detection element.

Surfaces of the primary unit and of the secondary unit may face eachother during operation of the IPT system. It is preferred that thedetector device comprises a plurality of detection elements which arearranged next to each other so as to define a detector area extending ina plane. They form an array of rows and columns, wherein each detectionelement defines a position in the array characterized by the ordinalnumbers of its row and its column. The detection elements are preferablyformed by in each case at least one winding of an electric line so as toform a coil. Each winding may have one turn or more than one turn. Theinterior areas enclosed by the winding or windings of each detectionelement may overlap or may not overlap. Preferably, the array ofdetection elements is oriented in a direction of the magnetic flux lineor lines at the highest flux density of the magnetic field produced bythe primary unit during operation of the IPT system. This direction mayextend perpendicularly to the plane mentioned above. In particular, thearea defined by the array may fully cover the area of the primary unitwindings and/or of the secondary unit windings. This means that thedetector device is capable of providing an image at least of the area inwhich the windings of the unit or units is placed. Preferably, the arraycovers—if viewed in the direction of the highest flux density of the IPTsystem—not only the windings, but also peripheral components of theunit, such as shields for shielding the environment from the field ofthe IPT system or magnetizable material.

In addition or alternatively to the configuration of the detector devicehaving a plurality of detection elements as mentioned above, thedetector device can be moved so as to scan the unit or arrangement to bedetected. For example, the detector device may be moved in the planementioned above. Alternatively, the orientation of the detector devicemay be changed in order to scan the unit or arrangement.

Comparing the signature with the detection result may reveal unexpecteddeviations. This indicates the presence of a foreign object and maytrigger an action, such as prohibiting or modifying the operation of theIPT system. In order to increase the reliability of the determination ofa deviation between signature and detection results, the material of thepotential foreign object may be determined from the detection results.

In addition or alternatively, the signature and the detection result maybe used to identify a specific specimen and/or a specific type of aprimary unit or of a secondary unit. Further in addition oralternatively, the signature and the detection result can be compared inorder to determine a positional deviation from an optimal relativeposition of the primary unit and the secondary unit. In this case, theresult of the comparison can be output to a motion control device whichcontrols motion of at least one of the primary and secondary unit sothat the optimal position is reached. The term “position” includes theorientation in this context.

One advantage of determining at least one electrical property of thedetector device, which property depends on the inductive or capacitivecoupling through the arrangement to be detected, is the fact that thedetection result does not significantly depend on the temperature.Another advantage is that the arrangement can be detected while itmoves. This applies to the relative motion of the primary and thesecondary unit mentioned above. This also applies to foreign objectswhich move in or into the air gap between the primary unit and thesecondary unit.

In particular, the following is proposed:

A method of detecting an arrangement comprising a primary unit of aninductive power transfer system and/or a secondary unit of the inductivepower transfer system, the method comprising:

-   -   using a detector device to detect the arrangement, the detector        device comprising at least one electrical conductor,    -   determining at least one electrical property of the detector        device and generating determination results consisting of a        determination result for each of different regions of the        arrangement,    -   comparing the determination results with existing information        about the arrangement to be detected, wherein the existing        information includes information about expected values for the        different regions of the arrangement, thereby generating a        comparison result,    -   deciding from the comparison result whether the determination        results indicate that the detector device has detected the        arrangement as expected.

The invention also covers a method of operating an inductive powertransfer system, comprising the method of detecting the arrangement,wherein an operation of the IPT is not started, is stopped or ismodified, if it is decided from the comparison result that thedetermination results do not indicate that the detector device hasdetected the arrangement as expected. For example, the arrangement isnot as expected if there is a foreign object or if the primary unit ofthe secondary unit is not the expected specimen or of the expected type.

Furthermore, a primary (first option) or secondary (second option) unitarrangement of an inductive power transfer system is proposed, thearrangement comprising:

-   -   a primary unit having a primary winding structure for generating        an electromagnetic field to be received by a secondary unit of        the inductive power transfer system in which an electric voltage        is induced by magnetic induction (first option), or a secondary        unit having a secondary winding structure for receiving an        electromagnetic field generated by a primary unit of the IPT        system (second option),    -   a detector device for detecting an arrangement comprising the        secondary unit (first option) or the primary unit (second        option), the detector device comprising an electrical conductor,    -   a determination unit for determining at least one electrical        property of the detector device for different regions of the        arrangement, thereby generating determination results consisting        of a determination result for different regions of the        arrangement,    -   a comparison unit for comparing the determination results with        existing information about the arrangement to be detected,        wherein the existing information includes information about        expected values for the different regions of the arrangement,        thereby generating a comparison result,    -   a decision unit for deciding from the comparison result whether        the determination results indicates that the detector device has        detected the arrangement as expected.

The determination result for each of the different regions of thearrangement may be a determined value (e.g. the value of an impedance orof an inductive or capacitive reactance) or a set of determined values(e.g. values at different frequencies) of the at least one electricalproperty. However, it is preferred that the determined value(s) is/arefurther processed in order to obtain the determination result. Forexample, the determined values for each region are classified so that adetermination result is obtained which indicates the predominantmaterial in the region of the arrangement.

The information about expected values for the different regions of thearrangement may be information derived from expected values of the atleast one electrical property to be determined. The information aboutexpected values of the at least one electrical property may consist ofthe material which is expected in the corresponding region of thearrangement.

As mentioned above, the detector device may comprise a plurality ofdetection elements. They may be used or adapted to detect thearrangement, wherein each detection element comprises an electricalconductor, wherein each of the plurality of detection elements isassigned to one or more than one of the different regions of thearrangement and wherein at least one electrical property of each of thedetection elements is determined, thereby generating the determinationresults consisting of a determination result for each of the detectionelements.

The arrangement may comprise a detection field antenna or, preferably, aplurality of detection field antennae, which may be used to generate anelectromagnetic detection field or electromagnetic detection fields,wherein the determination results are obtained in response to theelectromagnetic detection field(s). The electromagnetic detectionfield(s) couple(s) the arrangement to be detected with the detectordevice. According to one option, the detection field antenna(e) may beelement(s) in addition to the at least one detection element of thedetector device. If the detector device comprises a plurality of thedetection elements, there are separate field antennae and detectionelements. According to another option, the detection element(s) is/arethe field antenna(e). This means that the detection element(s) is/areused to generate the electromagnetic detection field(s). In any case,the field antenna(e) may be formed by in each case at least one windingof an electric conductor (in particular an electric line) so that eachfield antenna comprises a coil. The detection element(s) of the detectordevice and the field antenna(e) may carried by the same electric board.The windings of the electric lines of the detection element(s) and ofthe field antenna(e) may be strip conductors (e.g. printed) on theboard.

The primary unit or secondary unit arrangement may further comprise atleast one detection field generator for generating an electromagneticdetection field, the detection field generator having an alternatingvoltage source which is electrically coupled or can be coupled to atleast one detection field antenna, thereby forming an oscillatingcircuit in order to generate an electromagnetic detection field orelectromagnetic detection fields, wherein the determination results areobtained in response to the detection field(s).

Examples of the configuration and operation of an inductive detectionsystem are described in WO 2014/095722 A2 with reference to FIG. 1-13,18, 19 of the document. Individual detection elements and detectionfield antennae can be configured and operated in this manner. Examplesof the configuration and operation of arrays of detection windings aredescribed in WO 2014/095722 A2 with reference to FIG. 14-17 of thedocument. Arrays of detection elements and detection field antennae canbe configured and operated in this manner. However, the document doesnot disclose the concept of detecting a unit or an arrangement of an IPTsystem and comparing the detection result with a signature of the unitor of the arrangement.

It is preferred that the at least one electrical property depends on afrequency of an electromagnetic detection field, which couples thedetector device with the arrangement to be detected. In this case, theat least one electrical property (e.g. the inductive reactance of thedetection element inductively coupled to the assigned region of thearrangement) can be determined with respect to a plurality of frequencyvalues, thereby determining information on a frequency dependency of theat least one electrical property. The determination unit of the primaryunit or secondary unit arrangement may be adapted in this manner. Theinformation on the frequency dependency can then be used to identifydifferent materials of the arrangement. The underlying finding of thisembodiment is that the material properties (in particular the electricalconductivity, the magnetic permeability and the electron mobility)depend on the frequency of the electromagnetic field which couples thematerial to the detector device and that the dependency characterizesthe material. While some materials may have the same material propertyat a first frequency, they most likely have different materialproperties at another, second frequency. Therefore, the embodiment oftaking the frequency dependency into account is in particular applicableto the determination of the predominant material in a region of thearrangement to be detected as mentioned above. In particular, not onlythe fact that a specific material is predominant in the region can bedetermined, but the intensity, in particular the amplitude, of the atleast one electrical property can be determined. This intensity, inparticular amplitude, contains information about the amount andgeometrical extension of the material. As a consequence, the pixelsmentioned above may not only have one value, but two values or morevalues. For example, one value is the type of material and a secondvalue is a value characterizing the amount and/or geometrical extensionof the material.

Different physical effects may constitute the inductive and/orcapacitive coupling of the arrangement to be detected with the detectordevice. In particular, eddy currents are induced by the electromagneticdetection field(s) in electrically conductive material of thearrangement. In case of electrically non-conductive material, theelectrons in the material can be excited by the electromagneticdetection field(s) so as to perform oscillations. In both cases, theelectrons moving within the material produces an electromagnetic fieldwhich inductively and/or capacitively couples with the detector device.Corresponding magnetic effects also occur. In particular, theelectromagnetic detection field(s) cause(s) local magnetization of thematerial according to the material properties.

Another physical effect which may take place in particular in additionto the effects mentioned before is the excitation of electric currentsthrough the windings of the primary unit and/or secondary unit. Theseunits typically have at least one resonance frequency, i.e. anelectromagnetic field or an alternating voltage having the resonancefrequency produces an alternating electric current through the windingswith a high amplitude. Again, the electric current produces anelectromagnetic field which inductively and/or capacitively couples withthe detector device. The difference of electric currents through thewindings on one hand and eddy currents, electron oscillations and localmagnetisation on the other hand is the size of the region where theeffect occurs. The electric currents through the windings result in anearly homogeneous electromagnetic field within the area of thewindings, while the other effects depend on the local material. Thismeans that detection elements vis-à-vis the homogeneous area the same ornearly the same influence in case of an electric current through thewindings, but detect different influences depending on the localmaterial vis-à-vis the detection element in case of local effects. Bothinfluences may occur and may be detected simultaneously. However, if thefrequency dependency of the at least one electrical property of thedetector device is determined, the influence of an electric currentthrough the windings will provide the prevailing effect at or close to aresonance frequency of the windings and the local influences willprovide the prevailing effect otherwise. For these reasons, it ispreferred that the frequency dependency is considered for at least oneresonance frequency and, in addition, for at least one other frequency.Therefore, the signature also comprises the information about thisfrequency dependency. While the detection of the local material of theprimary or secondary unit is similar to the detection of metals andother materials in general, the detection of windings by evaluating theelectrical property of the detector device at or close to a resonancefrequency is a special feature. A foreign object interfering with theelectromagnetic detection field(s) can be detected in both cases. Itwould alter the determination results compared to the signature at orclose to the resonance frequency and otherwise.

According to a specific embodiment of the method, the at least oneelectrical property depends on a frequency of an electromagneticdetection field, which couples the detector device with the arrangementto be detected, wherein the at least one electrical property isdetermined with respect to a resonance frequency of a winding or ofwindings of at least one electrical conductor of the primary unit and/orthe secondary unit.

In particular, the determination unit may be adapted to determine the atleast one electrical property with respect to at least one frequency ofan electromagnetic detection field, which couples the detector devicewith the arrangement to be detected, wherein the at least one electricalproperty is determined with respect to one frequency or more than onefrequencies which is a resonance frequency or which are resonancefrequencies of a winding or of windings of at least one electricalconductor of the primary unit and/or the secondary unit.

The electromagnetic detection field(s) produced by the detection fieldantenna(e) may have a first oscillating frequency during a first mode ofoperation and may have a second oscillating frequency during a secondmode of operation. It is preferred that the modes of operation areperformed one after the other. Alternatively, the electromagneticfield(s) may have an oscillating frequency spectrum. In particular, theelectromagnetic field(s) may be generated at an oscillating frequency orat oscillating frequencies in the frequency range of 1 kHz to 5 MHz, inparticular in the range of 1 kHz to 500 kHz. Preferably, no oscillatingfrequency is smaller than 10 kHz. If electromagnetic fields aregenerated at single frequencies in different modes of operation (seeabove), these frequencies may be 10 kHz, 20 kHz, 30 kHz, whereinelectromagnetic field(s) having at least two of these frequencies aregenerated. Preferably, the IPT system is operated at a resonancefrequency of the secondary unit. In this case it is further preferredthat the electromagnetic detection field(s) is/are not generated at theresonance frequency. In particular, the frequency of the electromagneticdetection field(s) differs from the resonance frequency by at least 10kHz.

It should be noted that not only electrically conducting materials, suchas metals, can be detected by the detector device. Rather, since theelectron mobility is a material property which strongly influences theinductive and/or capacitive coupling of the material to the detectordevice, also electrically non-conductive materials can be detected. Inparticular, this applies to ferrites. A class of ferrites which can beused for IPT systems consists of electrically non-conductiveferrimagnetic ceramic compounds derived from iron oxides and/or fromoxides of other metals.

The determination results may be ordered according to a geometric orderof the different regions of the arrangement so as to prepare comparingthe determination results with the existing information. In particular,the geometric order is the order of the two-dimensional image havingpixels mentioned above. Therefore, the comparison may be made asprincipally known from comparisons of digital images.

The at least one deviation between the determination results and theexisting information may be detected and it may be decided that thearrangement comprises an additional object, which is part of thedetected arrangement in addition to the primary unit and/or secondaryunit.

A location of the additional object may be determined by determining acorresponding one or a corresponding plurality of the different regionsof the arrangement for which the determination result(s) deviate(s) fromthe existing information. The location may be output in order to controlthe operation of the IPT system and/or to inform an operator person or acentral system common to a plurality of IPT systems.

The determination results may be compared with existing informationabout a plurality of possible arrangements to be detected, wherein oneof the plurality of possible arrangements is identified as anarrangement actually detected by the plurality of detection elements.The arrangement is identified if its signature matches the determinationresults. Optionally, the matching signature and determination resultsmay be allowed to have a predetermined tolerance deviation which may bepredetermined for each of the different regions of the arrangementand/or for the total images.

Examples of the present invention will be described with reference tothe attached drawings in which:

FIG. 1 shows an IPT system with a detector device,

FIG. 2 schematically shows a secondary unit of an IPT system as viewedfrom the detector device on a primary side of the IPT system, inparticular the secondary unit of FIG. 1,

FIG. 3 shows an area on the right hand side of FIG. 2 as detected by thedetector device and

FIG. 4 shows the area of FIG. 3 and an additional foreign object asdetected by the detector device.

The IPT system 5 shown in FIG. 1 comprises a primary unit 7 embedded inthe ground and a secondary unit 34 being part of an on-board receivingunit on board a vehicle (not shown). During operation, the primary unit7 is provided with power from a primary side power converter 29 andgenerates an electromagnetic field, thereby transferring power to thesecondary unit 34.

A detector device 31 is placed above the primary unit 7 and below thesurface of a route 11, i.e. the detector device 31 is placed in betweenthe primary unit 7 and the secondary unit 34. A voltage generator 30 iselectrically connected to the detector device 31 and, for example,generates voltage pulses 32 which cause detection field antennae (notshown) integrated in the detector device 31 to generate electromagneticfields. Other than schematically shown in FIG. 1, the voltage generator30 may produce pulse width modulation signals. Generally speaking, thevoltage generator 30 may produce any desired frequency or range offrequencies. In particular, the electromagnetic detection field(s)produced by operating the voltage generator 30 may comprise at least oneresonance frequency of a winding of the secondary unit 34 and, inaddition, may comprise at least one further frequency so that resonantcurrents through the winding and local effects (e.g. eddy currents) inthe material of the secondary unit 34 are triggered.

The electromagnetic fields inductively couple the arrangement consistingof the secondary unit 34 and of a foreign object 4 on the surface of theroute 11 to the detector device 31. An evaluation device 36 is connectedto the detector device 31, which evaluation device 36 comprises adetermination unit for determining at least one electrical property ofthe detector device 31 for different regions of the arrangement 4, 34,comprises a comparison unit for comparing the determination results withexisting information about the arrangement 4, 34 to be detected andcomprises a decision unit deciding from the comparison result whetherthe determination results indicate that the detector device 31 hasdetected the secondary unit 34 as expected. Since there is the foreignobject 4, the secondary unit 34 has not been detected as expected.

If the foreign object 4 is an electrically conductive object eddycurrents are induced in the object 4 and interact with theelectromagnetic fields. Otherwise, depending on the electron mobility inthe object 4, it may interact with the electromagnetic fields by inducedoscillations of the electrons. Magnetisable objects interfere with themagnetic component of the electromagnetic fields. Only if the foreignobject 4 does not interact at all with the electromagnetic fields, itcannot be detected by the detector device 31. In this case, the foreignobject 4 does not interfere with the operation of the IPT system.

Several alternative embodiments and modifications to the embodimentshown in FIG. 1 are possible. For example, the detector device may becombined with the secondary unit and may be located at the lower surfaceof the secondary unit 34 shown in FIG. 1. Alternatively, a detectordevice may be combined with each of the primary and secondary unit. Inany case, it is preferred that the detector device(s) is/are placed inbetween the primary unit and the secondary unit.

In FIG. 2, the structure of a secondary unit 34 is shown as can bedetected by a detector device on the primary side of the IPT system. Thesecondary unit comprises a plurality of coils of electric lines whichare referred to as windings 43 that form the winding structure of thesecondary unit 34. In the viewing direction behind the windings 43shields 41 of magnetizable material, in particular of ferrite, areplaced. There are four shields 41 and in front of each shield 41, threewindings 43 are placed. The windings 43 extend in parallel to each otherin a longitudinal direction, the direction from top to bottom in FIG. 2.The structural groups comprising one shield 41 and three windings 43 areplaced next to each other in the lateral direction perpendicular to thelongitudinal direction.

A detector device, such as the detector device 31 of FIG. 1, preferablydetects the whole structure shown in FIG. 2 and produces detectedinformation for a plurality of regions of the structure, which can beprocessed to form a two-dimensional image of the structure. Each regionresults in a pixel of a two-dimensional image. A processing unit, e.g.the evaluation device 36 of FIG. 1, may be combined with the detectordevice which performs the processing steps necessary to form the imagefrom the information detected by the detector device. The image may berepresented by digital data in any form suitable for digitaltwo-dimensional images. Analogue information about the at least oneelectrical property of the detector device, in particular of theindividual detection elements of the detector device, is output from thedetector device to an analogue/digital converter which converts theanalogue information into digital information and outputs the digitalinformation to the processing unit. It may be in practice, for example,a field programmable gate array (FPGA), a personal computer or anotherdigital computing unit. The processing unit processes the receiveddigital information and thereby generates the detection results. Forexample, it determines for each of the detection elements the phaseangle and amplitude of the impedance of the detection element, inparticular by evaluating the amplitude of the current through thedetection element and the amplitude of the voltage across the detectionelement. In this case, the analogue information provided by the detectordevice comprises corresponding measurement values. Alternatively, otherprocedures for determining the impedance or inductive or capacitivereactance of the detection element can be performed. Preferably, theelectrical property, which may be at least one of the electricalquantities mentioned, is determined at a plurality of frequency valuesof the frequency of the current through the detection element and of thevoltage across the detection element.

In any case, it is preferred that for each region of the detectedstructure, in particular for each detection element which is assigned toone of the regions, the predominant material in the region isdetermined.

A corresponding image comprising pixels of the detected structure isshown in FIG. 3. For simplicity, only a part of the complete image isshown, namely the part which corresponds to the area on the right handside in FIG. 2, where the shield 41 on the right hand side behind threeof the windings 43 is located. This area in FIG. 2 shows the gridillustrated by dashed lines which corresponds to the partial image shownin FIG. 3. While the grid in FIG. 2 separates the individual regions ofthe structure which are detected by the detector device, the grid inFIG. 3 separates the pixels of the partial image obtained. Each pixel inFIG. 3 has a value which characterizes the predominant material in thecorresponding region of the structure. In the example shown, the partialarea has only two different predominant materials, namely copper of thewindings 43 indicated by “C” and ferrite of the shield 41 indicated by“F”.

If the foreign object 4 shown in FIG. 1 is present below the partialarea which is represented by the partial image and if the foreign objectinterferes with the electromagnetic fields generated for detecting thestructure, the material of the foreign object 4 is also detected, forexample iron, and the pixels in the partial image which correspond tothe region or regions of the foreign object 4 have the value “I” foriron (see FIG. 4) instead of the copper or ferrite shown in FIG. 3.While the partial image shown in FIG. 3 is identical to the signature ofthe structure, the modified image shown in FIG. 4 comprises pixelshaving the value “I”. Therefore, the obtained image does not correspondto the signature. Consequently, the foreign object can be detected bycomparing the image which is the signature of the structure with theimage produced by the detector device and the processing unit. For thecomparison, known methods of comparing digital images can be performedby a comparison unit implemented in the processing unit and a decisionunit also implemented in the processing unit decides that there is adeviation between the signature and the image taken. In particular, thedecision unit may output a deviation signal to a control of the IPTsystem, for example to a control of the power converter 29 shown in FIG.1 and the control may switch off the primary unit, in particular bystopping operation of the power converter.

1. A method of detecting an arrangement comprising a primary unit of aninductive power transfer system and/or a secondary unit of the inductivepower transfer system, wherein the primary unit comprises a primarywinding structure for generating a magnetic or electromagnetic field tobe received by the secondary unit, wherein the secondary unit has asecondary winding structure in which an electric voltage is induced whenthe magnetic or electromagnetic field is received and wherein the methodcomprises: using a detector device to detect the arrangement, thedetector device comprising at least one electrical conductor,determining at least one electrical property of the detector device andgenerating determination results consisting of a determination resultfor each of different regions of the arrangement, comparing thedetermination results with existing information about a signature, whichsignature is characteristic for the arrangement to be detected, whereinthe existing information includes information about expected values forthe different regions of the arrangement, thereby generating acomparison result, deciding from the comparison result whether thedetermination results indicate that the detector device has detected thearrangement as expected, thereby identifying the arrangement comprisingthe primary unit and/or the secondary unit wherein different types ofprimary units have different signatures and/or different types ofsecondary units have different signatures and wherein the arrangementcomprising a primary unit of a specific type of primary units and/or asecondary unit of a specific type of secondary units, for which specifictype of primary units and/or specific type of secondary unitsinformation about its signature exists, is identified by deciding fromthe comparison result whether the determination results indicate thatthe detector device has detected the arrangement comprising the primaryunit of the specific type of primary units and/or the secondary unit ofthe specific type of secondary units.
 2. The method of claim 1, whereina plurality of detection elements of the detector device is used todetect the arrangement, wherein each detection element comprises anelectrical conductor, wherein each of the plurality of detectionelements is assigned to one or more than one of the different regions ofthe arrangement and wherein at least one electrical property of each ofthe detection elements is determined, thereby generating thedetermination results consisting of a determination result for each ofthe detection elements.
 3. The method of claim 1, wherein a plurality ofdetection field antennae are used to generate an electromagneticdetection field or electromagnetic detection fields and wherein thedetermination results are obtained in response to the electromagneticdetection field.
 4. The method of claim 1, wherein the at least oneelectrical property depends on a frequency of an electromagneticdetection field, which couples the detector device with the arrangementto be detected, wherein the at least one electrical property isdetermined with respect to a plurality of frequency values, therebydetermining information on a frequency dependency of the at least oneelectrical property, and wherein the information on the frequencydependency is used to identify different materials of the arrangement.5. The method of claim 1, wherein the at least one electrical propertydepends on a frequency of an electromagnetic detection field, whichcouples the detector device with the arrangement to be detected, whereinthe at least one electrical property is determined with respect to aresonance frequency of a winding or of windings of at least oneelectrical conductor of the primary unit and/or the secondary unit. 6.The method of claim 1, wherein the determination results are orderedaccording to a geometric order of the different regions of thearrangement so as to prepare comparing the determination results withthe existing information.
 7. The method of claim 1, wherein at least onedeviation between the determination results and the existing informationis detected and it is decided that the arrangement comprises anadditional object, which is part of the detected arrangement in additionto the primary unit and/or secondary unit.
 8. The method of claim 7,wherein a location of the additional object is determined by determininga corresponding one or a corresponding plurality of the differentregions of the arrangement for which the determination result deviatesfrom the existing information.
 9. The method of claim 1, wherein thedetermination results are compared with existing information about aplurality of possible arrangements to be detected and wherein one of theplurality of possible arrangements is identified as an arrangementactually detected by the plurality of detection elements.
 10. (canceled)11. The method of claim 1, wherein different primary units of a sametype of primary units have different individual signatures and/ordifferent secondary units of a same type of secondary units havedifferent individual signatures and wherein the arrangement comprising aspecific primary unit of the same type of primary units and/or aspecific secondary unit of the same type of secondary units, for whichspecific primary unit and/or specific secondary unit information aboutits individual signature exists, is identified by deciding from thecomparison result whether the determination results indicate that thedetector device has detected the arrangement comprising the specificprimary unit of the same type of primary units and/or the specificsecondary unit of the same type of secondary units.
 12. A method ofoperating an inductive power transfer system, comprising the method ofclaim 1, wherein an operation of the inductive power transfer system isnot started, is stopped or is modified, if it is decided from thecomparison result that the determination results do not indicate thatthe detector device has detected the arrangement as expected.
 13. Aprimary unit arrangement of an inductive power transfer system,comprising: a primary unit having a primary winding structure forgenerating a magnetic or electromagnetic field to be received by asecondary unit of the inductive power transfer system in which anelectric voltage is induced by magnetic induction, a detector device fordetecting an arrangement comprising the secondary unit, the detectordevice comprising an electrical conductor, a determination unit fordetermining at least one electrical property of the detector device fordifferent regions of the arrangement, thereby generating determinationresults consisting of a determination result for different regions ofthe arrangement, a comparison unit for comparing the determinationresults with existing information about a signature, which signature ischaracteristic for the arrangement to be detected, wherein the existinginformation includes information about expected values for the differentregions of the arrangement, thereby generating a comparison result, adecision unit for deciding from the comparison result whether thedetermination results indicates that the detector device has detectedthe arrangement as expected, thereby identifying the arrangementcomprising the secondary unit wherein different types of secondary unitshave different signatures and wherein the decision unit is adapted toidentify the arrangement comprising the secondary unit of a specifictype of secondary units, for which specific type of secondary unitsinformation about its signature exists, by deciding from the comparisonresult of the comparison unit whether the determination results indicatethat the detector device has detected the arrangement comprising thesecondary unit of the specific type of secondary units.
 14. A secondaryunit arrangement of an inductive power transfer system, comprising: asecondary unit having a secondary winding structure for receiving amagnetic or electromagnetic field generated by a primary unit of theinductive power transfer system and for producing an electric voltage bymagnetic induction, a plurality of detection elements for detecting anarrangement comprising the primary unit, the detector device comprisingan electrical conductor, a determination unit for determining at leastone electrical property of the detector device with respect to differentregions of the arrangement, thereby generating determination resultsconsisting of a determination result for different regions of thearrangement, a comparison unit for comparing the determination resultswith existing information about the arrangement to be detected, whereinthe existing information includes information about expected values forthe different regions of the arrangement, thereby generating acomparison result, a decision unit for deciding from the comparisonresult whether the determination results indicates that the detectordevice has detected the arrangement as expected, thereby identifying thearrangement comprising the primary unit wherein different types ofprimary units have different signatures and wherein the decision unit isadapted to identify the arrangement comprising the primary unit of aspecific type of primary units, for which specific type of primary unitsinformation about its signature exists, by deciding from the comparisonresult of the comparison unit whether the determination results indicatethat the detector device has detected the arrangement comprising theprimary unit of the specific type of primary units.
 15. The primary unitarrangement of claim 13, wherein the detector device has a plurality ofdetection elements, each detection element comprising an electricalconductor, wherein the determination unit is adapted to determine atleast one electrical property of each of the detection elements, therebygenerating the determination results consisting of a determinationresult for each of the detection elements.
 16. The primary unitarrangement of claim 13, further comprising at least one detection fieldgenerator for generating an electromagnetic detection field, thedetection field generator having an alternating voltage source which iselectrically coupled or can be coupled to at least one detection fieldantenna, thereby forming an oscillating circuit in order to generate anelectromagnetic detection field or electromagnetic detection fields,wherein the determination results are obtained in response to thedetection fields.
 17. The primary unit arrangement of claim 13, whereinthe determination unit is adapted to determine the at least oneelectrical property with respect to a plurality of frequency values ofan electromagnetic detection field, which couples the detector devicewith the arrangement to be detected, thereby determining information ona frequency dependency of the at least one electrical property, and isadapted to identify different materials of the arrangement from theinformation on the frequency dependency.
 18. The primary unitarrangement of claim 13, wherein the determination unit is adapted todetermine the at least one electrical property with respect to at leastone frequency of an electromagnetic detection field, which couples thedetector device with the arrangement to be detected, wherein the atleast one electrical property is determined with respect to onefrequency or more than one frequencies which is a resonance frequency orwhich are resonance frequencies of a winding or of windings of at leastone electrical conductor of the primary unit.
 19. (canceled)
 20. Theprimary unit arrangement of claim 13, wherein different primary units ofa same type of primary units have different individual signatures andwherein the decision unit is adapted to identify the arrangementcomprising a specific primary unit of the same type of primary units,for which specific primary unit information about its individualsignature exists, by deciding from the comparison result of thecomparison unit whether the determination results indicate that thedetector device has detected an arrangement comprising the specificprimary unit of the same type of primary units.
 21. The secondary unitarrangement of claim 14, further comprising at least one detection fieldgenerator for generating an electromagnetic detection field, thedetection field generator having an alternating voltage source which iselectrically coupled or can be coupled to at least one detection fieldantenna, thereby forming an oscillating circuit in order to generate anelectromagnetic detection field or electromagnetic detection fields,wherein the determination results are obtained in response to thedetection fields.
 22. The secondary unit arrangement of claim 14,wherein the determination unit is adapted to determine the at least oneelectrical property with respect to a plurality of frequency values ofan electromagnetic detection field, which couples the detector devicewith the arrangement to be detected, thereby determining information ona frequency dependency of the at least one electrical property, and isadapted to identify different materials of the arrangement from theinformation on the frequency dependency.
 23. The secondary unitarrangement of claim 14, wherein the determination unit is adapted todetermine the at least one electrical property with respect to at leastone frequency of an electromagnetic detection field, which couples thedetector device with the arrangement to be detected, wherein the atleast one electrical property is determined with respect to onefrequency or more than one frequencies which is a resonance frequency orwhich are resonance frequencies of a winding or of windings of at leastone electrical conductor of the secondary unit.
 24. The secondary unitarrangement of claim 14, wherein different secondary units of a sametype of secondary units have different individual signatures and whereinthe decision unit is adapted to identify the arrangement comprising aspecific secondary unit of the same type of secondary units, for whichspecific secondary unit information about its individual signatureexists, by deciding from the comparison result of the comparison unitwhether the determination results indicate that the detector device hasdetected an arrangement comprising the specific secondary unit of thesame type of secondary units.